Hybrid CuSn nanosphere-functionalized Cu/Sn co-doped hollow carbon nanofibers as anode materials for sodium-ion batteries.

To strengthen the electrochemical performance of anode materials for sodium-ion batteries, Cu/Sn co-doped hollow carbon nanofibers functionalized by hybrid CuSn nanospheres (CuSn/C@MCNF) were prepared by a simple electrospinning method. The microstructural characteristics of CuSn/C@MCNF confirmed the same doped elements and strong interactions in hybrid CuSn nanospheres and the hollow carbon nanofiber substrate. CuSn/C@MCNF has superior specific capacity, excellent conductivity and high cycling stability. In particular, the doped hollow carbon nanofiber substrate can facilitate Na+ transport and alleviate volume expansion during the process of sodium storage. When applied as an anode material for sodium-ion batteries, CuSn/C@MCNF can deliver a reversible capacity of 340.1 mA h g-1 at a large current density of 1 A g-1 for 1000 cycles and a high-rate capacity of 202.5 mA h g-1 at 4.0 A g-1, all superior to the corresponding Sn-SnOx@MCNF- and MCNF-based electrodes. This work provides a basic idea for future anode materials in high-performance sodium-ion batteries.

Two Birds One Stone: Graphene Assisted Reaction Kinetics and Ionic Conductivity in Phthalocyanine-Based Covalent Organic Framework Anodes for Lithium-ion Batteries.

This work reports a covalent organic framework composite structure (PMDA-NiPc-G), incorporating multiple-active carbonyls and graphene on the basis of the combination of phthalocyanine (NiPc(NH2 )4 ) containing a large π-conjugated system and pyromellitic dianhydride (PMDA) as the anode of lithium-ion batteries. Meanwhile, graphene is used as a dispersion medium to reduce the accumulation of bulk covalent organic frameworks (COFs) to obtain COFs with small-volume and few-layers, shortening the ion migration path and improving the diffusion rate of lithium ions in the two dimensional (2D) grid layered structure. PMDA-NiPc-G showed a lithium-ion diffusion coefficient (DLi + ) of 3.04 × 10-10 cm2 s-1 which is 3.6 times to that of its bulk form (0.84 × 10-10 cm2 s-1 ). Remarkably, this enables a large reversible capacity of 1290 mAh g-1 can be achieved after 300 cycles and almost no capacity fading in the next 300 cycles at 100 mA g-1 . At a high areal capacity loading of ≈3 mAh cm-2 , full batteries assembled with LiNi0.8 Co0.1 Mn0.1 O2 (NCM-811) and LiFePO4 (LFP) cathodes showed 60.2% and 74.7% capacity retention at 1 C for 200 cycles. Astonishingly, the PMDA-NiPc-G/NCM-811 full battery exhibits ≈100% capacity retention after cycling at 0.2 C. Aided by the analysis of kinetic behavior of lithium storage and theoretical calculations, the capacity-enhancing mechanism and lithium storage mechanism of covalent organic frameworks are revealed. This work may lead to more research on designable, multifunctional COFs for electrochemical energy storage.

Phenediamine bridging phthalocyanine-based covalent organic framework polymers used as anode materials for lithium-ion batteries.

In this study, phenediamine bridging phthalocyanine-based covalent organic framework materials (CoTAPc-PDA, CoTAPc-BDA and CoTAPc-TDA) with increasingly-widening pore sizes are prepared by reacting cobalt octacarboxylate phthalocyanine with p-phenylenediamine (PDA), benzidine (BDA) and 4,4''-diamino-p-terphenyl (TDA), respectively. The effects of frame size on the morphology structure and its electrochemical properties were explored. X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) images show that the pore sizes of the CoTAPc-PDA, CoTAPc-BDA and CoTAPc-TDA are about 1.7 nm, 2.0 nm and 2.3 nm, respectively, which are close to the simulated results after geometric conformation optimization using Material Studio software. In addition, the specific surface areas of CoTAPc-PDA, CoTAPc-BDA and CoTAPc-TDA are 62, 81 and 137 m2 g-1, respectively. With increase in the frame size, the specific surface area of the corresponding material increases, which is bound to produce different electrochemical behaviors. Consequently, the initial capacities of the CoTAPc-PDA, CoTAPc-BDA and CoTAPc-TDA electrodes in lithium-ion batteries (LIBs) are 204, 251 and 382 mA h g-1, respectively. As the charge and discharge processes continue, the active points in the electrode material are continuously activated, leading to a continuous increase in charge and discharge capacities. After 300 cycles, the CoTAPc-PDA, CoTAPc-BDA and CoTAPc-TDA electrodes exhibit capacities of 519, 680 and 826 mA h g-1, respectively, and after 600 cycles, the capacities are maintained at 602, 701 and 865 mA h g-1, respectively, with a stable capacity retention rate at a current density of 100 mA g-1. The results show that the large-size frame structure materials have a larger specific surface area and more favorable lithium ion transmission channels, which produce greater active point utilization and smaller charge transmission impedance, thus showing larger charge and discharge capacity and superior rate capability. This study fully confirms that frame size is a key factor affecting the properties of organic frame electrodes, providing design ideas for the development of high-performance organic frame electrode materials.

Compressibility and crystalline structures of PVDF membranes under elevated gravity acceleration by two-axis spin coating technology.

Polymers play an important role in designing and manufacturing lithium-ion batteries and sensors. This study investigates the compressibility and crystalline structure of polyvinylidene fluoride (PVDF) membranes spin-coated under different gravity conditions. Particle Flow Code (PFC) numerically models the compressibility of membranes. The models show a 10% reduction in the thickness of the membrane when the gravity is artificially elevated to 500g. The time of solvents' release from the free surface of membranes based on Stokes' law is simulated by MATLAB. The results show that the solvents' release time decreases significantly when the artificial gravity increases. Novel experiments are conducted to validate the results of numerical modeling and MATLAB simulations. Four PVDF membranes are spin-coated by a novel two-axis spin coater under 1, 100, 300, and 500g. The SEM images experimentally report a 21% reduction in the thickness of the membrane spin-coated under 500g. The weights of membranes are measured to verify the results of MATLAB simulations. The results show that 99% of the whole solvents are evaporated while increasing the gravity to noticeable values. XRD, FTIR, and SEM characterize the polymeric crystalline structure of membranes. The crystalline structure of spin-coated PVDF membranes varies under various gravity conditions. The XRD measurements report phase transitions, while the gravity is artificially elevated during membranes' fabrication. FTIR spectroscopy revealed that the observed phase transition is from γ toward ß while increasing the gravity acceleration.

A two-dimensional MXene/BN van der Waals heterostructure as an anode material for lithium-ion batteries.

Titanium carbide (Ti3C2Tx) is highly regarded as a promising anode material for lithium-ion batteries but suffers from sluggish kinetics with low storage capacity. In this work, a BN/Ti3C2Tx heterostructure is effectively fabricated by high energy ball-milling, which plays a series of roles in enlarging the interlayer spacing, reducing the size of the nanosheets and maintaining the structural integrity. Benefiting from the synergistic effect between the BN and Ti3C2Tx monolayers, it delivers a high reversible capacity of 521.6 mA h g-1 at 0.1 A g-1, excellent rate capabilities (344.9 mA h g-1 at 1 A g-1 and 251.3 mA h g-1 at 2.5 A g-1) and a robust long-term cycling stability with 84.4% capacity retention after 1400 cycles. In particular, the theoretical calculations further confirm that the BN/Ti3C2Tx heterostructure manifests improved adsorption energies, an ultralow diffusion barrier and a high charge-discharge rate. These findings provide an important new strategy for further design and rational fabrication of MXenes for energy storage applications.

Induction and Maintenance of Local Structural Durability for High-Energy Nickel-Rich Layered Oxides.

Nickel-rich layered oxides are one of the most promising cathode candidates for next-generation high-energy-density lithium-ion batteries. However, due to similar ion radius between Li+ and Ni2+ (0.76 and 0.69 Å), the Li+ /Ni2+ mixing phenomenon seriously hinders the migration of Li+ and increases kinetic barrier of Li+ diffusion, resulting in limited rate capability. In this work, the introduction of Ce4+ to effectively improve electrochemical properties of Ni-rich cathode materials is proposed. The LiNi0.8 Co0.15 Al0.05 O2 (LNCA) is modified with an additional precursor oxidization process using an appropriate amount of (NH4 )2 Ce(NO3 )6 . The Ce(NO3 )6 2- easily obtains electrons and generates reduction reactions, while Ni(OH)2 is prone to electron loss and oxidation reaction. The participation of (NH4 )2 Ce(NO3 )6 can promote the oxidation of Ni2+ to Ni3+ , thereby reducing the Li+ /Ni2+ mixing and increasing the structural stability of LNCA samples. Ce4+ cation doping can impede Li+ /Ni2+ mixing of LNCA cathode materials upon the long-term cycles. Both rate performance and long-term cyclability of Li[Ni0.8 Co0.15 Al0.05 ]0.97 Ce0.03 O2 (LNCA-Ce0.03) sample are significantly improved. Besides, a practical pouch cell based on the cathode presents sufficient gravimetric energy density (≈300 Wh kg-1 ) and cycling stability (capacity retention of 81.3% after 500 cycles at 1 C).

A phthalocyanine-grafted MA-VA framework polymer as a high performance anode material for lithium/sodium-ion batteries.

A porous MA-VA-PcNi polymer was prepared by grafting nickel phthalocyanine (PcNi) onto the main chain of a maleic anhydride-vinyl acetate (MA-VA) polymer, and an MA-VA-PcNi electrode is prepared by electrospinning technology to inhibit the agglomeration of the active powder effectively, which produces spherical particles with a diameter of 100-300 nm. The synthesized MA-VA-PcNi polymer is used as the anode for lithium-ion and sodium-ion batteries, exhibiting excellent energy storage behaviors. The MA-VA-PcNi/Li battery displays a high capacity of 610 mA h g-1 and can still remain at 507 mA h g-1 with a retention rate of 83.1% after 400 cycles at a current density of 200 mA g-1. Even at a high current density of 2 A g-1, the specific capacity can remain at 195 mA h g-1. In addition, the MA-VA-PcNi/Na battery displays a high capacity of 336 mA h g-1 and can still remain at 278 mA h g-1 with a retention rate of 82.7% after 400 cycles at a current density of 100 mA g-1. A high specific capacity of 164 mA h g-1 can also be achieved at a high current density of 1 A g-1. After nickel phthalocyanine (PcNi) was grafted onto the MA-VA polymer, aggregation between phthalocyanine rings was effectively prevented, and this exposes more active sites. At the same time, the spherical particles obtained by electrospinning technology further improve the dispersion and increase the number of active sites of the active materials. Finally, the electrode materials show excellent energy storage behavior for lithium-ion and sodium-ion batteries, which provides a new idea for designing high-performance energy storage materials for organic electrodes.

Tetraethylthiophene-2,5-diylbismethylphosphonate: A Novel Electrolyte Additive for High-Voltage Batteries.

In this work, a novel high-voltage electrolyte additive, tetraethylthiophene-2,5-diylbismethylphosphonate (TTD), was synthesized, and the influence of TTD on the electrolyte and its electrochemical performance under different voltages were studied by changing the content of the TTD additive. The results showed that the TTD additive significantly improved the capacity, cycle stability, and rate capability of batteries when charging/discharging at high voltages. After adding 1 % TTD to the basic electrolyte, the capacity retention rate of batteries after 200 cycles at 4.2, 4.3, 4.4, and 4.5 V increased by 20.8, 18.3, 50, and 31.9 %, respectively. In addition, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results showed that TTD could effectively inhibit the decomposition of the electrolyte and participate in the formation of a uniform, thin, and stable cathode electrolyte interphase (CEI) film on the electrode surface, thereby effectively inhibiting the side reaction between the electrolyte decomposition product and the CEI membrane, and finally improving the high-voltage performance of the battery. The TTD additive may provide a cost-effective solution for high-performance high-voltage electrolytes.

The effects of Al-doped to cathode material based on hollow microspheres of nickel-manganese on sodium-ion batteries.

Sodium-ion batteries (SIBs) are expected to be a great substitute for lithium ion batteries. Although there are many difficulties to overcome, SIBs have become one of the most important research areas for large-scale energy storage equipment. The spherical particles are conducive to the contact between the cathode material and the electrolyte, which could increase the electrochemical reaction area, and improve the deintercalation rate of sodium ions during charging and discharging. In this paper, a precipitation method was used to prepare spherical MnCO3material as template and raw material. After all the raw materials were weighed with the molar ratios of Na0.67Mn0.67-0.75xNi0.33AlxO2, a series of hollow micro-spherical sodium-ion cathode materials were synthesized by the conventional high-temperature solid-state method. The effects of Al-doped on the structure and electrochemical performance of Na0.67Ni0.33Mn0.67O2was studied, and it was founded that the samples doped with Al had smaller particle size than that without Al. The electrochemical tests showed that Na0.67Mn0.595Ni0.33Al0.1O2(x= 0.1) exhibite superior high-rate capabilities and cyclic stability. And the hollow microsphere structure has a higher capacity, the first discharge capacity at 0.1C reach 128 mAh g-1.

Graphene composite 3,4,9,10-perylenetetracarboxylic sodium salts with a honeycomb structure as a high performance anode material for lithium ion batteries.

In order to address the issues of high solubility in electrolytes, poor conductivity and low active site utilization of organic carbonyl electrode materials, in this work, the 3,4,9,10-perylenetetracarboxylic sodium salt (PTCDA-Na) and its graphene composite PTCDA-Na-G are prepared by the hydrolysis of 3,4,9,10-perylenetetracarboxylic dianhydride and the strategy of antisolvent precipitation. The obtained PTCDA-Na active substance has a porous honeycomb structure, showing a large specific surface area. Moreover, after recombination with graphene, the dispersion and specific surface area of PTCDA-Na are further enhanced, and more active sites are exposed and conductivity is improved. As a result, the PTCDA-Na-G composite electrode materials exhibit superior electrochemical energy storage behaviors. The initial charge capacity of the PTCDA-Na-G electrode is 890.5 mA h g-1, and after 200 cycles, the capacity can still remain at 840.0 mA h g-1 with a high retention rate of 94.3%, which is much larger than those of the PTCDA-Na electrode. In addition, at different current densities, the PTCDA-Na-G electrode also presents higher capacities and better cycle stability than the PTCDA-Na electrode. Compared with PTCDA-Na with a porous honeycomb structure and previously reported sodium carboxylic acid salts with a large size bulk structure, the PTCDA-Na-G composite material prepared in this work shows superior electrochemical energy storage properties due to its large specific surface area, high dispersion, more exposed active sites and large electrical conductivity, which would provide new ideas for the development of high performance organic electrode materials for lithium-ion batteries.

1,4,5,8-Naphthalenetetracarboxylic dianhydride grafted phthalocyanine macromolecules as an anode material for lithium ion batteries.

For solving the problems of high solubility in electrolytes, poor conductivity and low active site utilization of organic electrode materials, in this work, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) grafted nickel phthalocyanine (TNTCDA-NiPc) was synthesized and used as an anode material for lithium ion batteries. As a result, the dispersibility, conductivity and dissolution stability are improved, which is conducive to enhancing the performance of batteries. The initial discharge capacity of the TNTCDA-NiPc electrode is 859.8 mA h g-1 at 2 A g-1 current density, which is much higher than that of the NTCDA electrode (247.4 mA h g-1). After 379 cycles, the discharge capacity of the TNTCDA-NiPc electrode is 1162.9 mA h g-1, and the capacity retention rate is 135.3%, which is 7 times that of the NTCDA electrode. After NTCDA is grafted to the phthalocyanine macrocyclic system, the dissolution of the NTCDA in the electrolyte is reduced, and the conductivity and dispersion of the NTCDA and phthalocyanine ring are also improved, so that more active sites of super lithium intercalation from NTCDA and phthalocyanine rings are exposed, which results in better electrochemical performance. The strategy of grafting small molecular active compounds into macrocyclic conjugated systems used in this work can provide new ideas for the development of high performance organic electrode materials.

Porous diatomite-mixed 1,4,5,8-NTCDA nanowires as high-performance electrode materials for lithium-ion batteries.

A porous composite electrode composed of diatomite-mixed 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) is prepared by electrostatic spinning technology. Compared with traditional coated electrodes without diatomite mixing, the obtained composite electrode materials have higher porosity, larger specific surface area and faster lithium ion transport channels, which makes them exhibit better electrochemical performance, such as smaller impedance, higher capacity, and better cycling stability and rate performance. The electrospun diatomite-mixed 1,4,5,8-NTCDA composite (ED-1,4,5,8-NTCDA) electrode shows an initial coulombic efficiency of 77.2%, which is much higher than that of the electrospun 1,4,5,8-NTCA (E-1,4,5,8-NTCDA) electrode without diatomite mixing (63.8%) and the coated 1,4,5,8-NTCA (C-1,4,5,8-NTCDA) electrode (48.3%). Moreover, the ED-1,4,5,8-NTCDA electrode displays an initial discharge capacity of 1106.5 mA h g-1, which is much higher than that of the E-1,4,5,8-NTCDA electrode (546.0 mA h g-1) and the C-1,4,5,8-NTCDA electrode (185.4 mA h g-1). After 200 cycles, the capacity of the ED-1,4,5,8-NTCDA electrode remains at 1008.5 mA h g-1 with a retention ratio of 91.2%, which is also much higher than that of 753.2 mA h g-1 for the E-1,4,5,8-NTCDA electrode and 288.1 mA h g-1 for the C-1,4,5,8-NTCDA electrode. Even at a higher current density of 1500 mA g-1, its capacity remains above 508.9 mA h g-1. The ED-1,4,5,8-NTCDA electrode presents superior performance, which opens up a promising new approach for further utilization of organic materials as electrode materials in rechargeable lithium-ion batteries.

First principles study of surface properties and oxygen adsorption on the surface of Al3Ti intermetallic alloys.

The density functional theory (DFT) method was applied to study the structural, electronic and surface properties of low-index Al3Ti intermetallic materials. The surface energies and electronic structures of those surfaces were also discussed in this study. The calculated surface energies of the low-index surfaces of Al3Ti indicated that nonstoichiometric (110) surface with Al termination was the most stable surface. On this basis, the oxygen adsorption behavior of the (110)-Al surface was further studied to clarify the antioxidant mechanism of Al3Ti intermetallic alloys. Various adsorption sites of oxygen atoms on the (110)-Al surface were considered to identify the most stable adsorption configurations. According to the calculation results of adsorption energies, it was found that stability was maximized when oxygen was adsorbed at the Al-Al bridge site. Meanwhile, a density of state study indicated that adsorption of oxygen on the (110)-Al surface preferred to bond with Al atoms rather than Ti atoms.

Ultrahigh-Energy Density Lithium-Ion Cable Battery Based on the Carbon-Nanotube Woven Macrofilms.

Moore's law predicts the performance of integrated circuit doubles every two years, lasting for more than five decades. However, the improvements of the performance of energy density in batteries lag far behind that. In addition, the poor flexibility, insufficient-energy density, and complexity of incorporation into wearable electronics remain considerable challenges for current battery technology. Herein, a lithium-ion cable battery is invented, which is insensitive to deformation due to its use of carbon nanotube (CNT) woven macrofilms as the charge collectors. An ultrahigh-tap density of 10 mg cm-2 of the electrodes can be obtained, which leads to an extremely high-energy density of 215 mWh cm-3 . The value is approximately seven times than that of the highest performance reported previously. In addition, the battery displays very stable rate performance and lower internal resistance than conventional lithium-ion batteries using metal charge collectors. Moreover, it demonstrates excellent convenience for connecting electronics as a new strategy is applied, in which both electrodes can be integrated into one end by a CNT macrorope. Such an ultrahigh-energy density lithium-ion cable battery provides a feasible way to power wearable electronics with commercial viability.

Stabilization of Garnet/Liquid Electrolyte Interface Using Superbase Additives for Hybrid Li Batteries.

To improve the solid-electrolyte/electrode interface compatibility, we have proposed the concept of hybrid electrolyte by including a small amount of liquid electrolyte in between. In this work, n-BuLi, a superbase, has been found to significantly improve the cycling performance of LiFePO4/Li hybrid cells containing Li7La3Zr1.5Ta0.5O12 (LLZT) and conventional carbonate-based liquid electrolyte. The modified cells have been cycled for 400 cycles at 100 and 200 µA cm-2 at room temperature, indicating excellent solid/liquid electrolyte interface stability. The role of n-BuLi may be 3-fold: to retard the decomposition reaction of LE, to suppress the Li+/H+ exchange, and to lithiate the garnet/LE interface, inhibiting side reactions and enhancing interfacial lithium-ion transport.

Li-Ion Conduction and Stability of Perovskite Li3/8Sr7/16Hf1/4Ta3/4O3.

A solid Li-ion conductor with a high room temperature Li-ion conductivity and small interfacial resistance is required for its application in next-generation Li-ion batteries. Here, we prepared a cubic perovskite-related oxide with the general formula Li3/8Sr7/16Hf1/4Ta3/4O3 (LSHT) by a conventional solid-state reaction method, which was studied by X-ray diffraction, electrochemical impedance spectroscopy, and (7)Li MAS NMR. Li3/8Sr7/16Hf1/4Ta3/4O3 has a high Li-ion conductivity of 3.8 × 10(-4) S cm(-1) at 25 °C and a low activation energy of 0.36 eV in the temperature range 298-430 K. It exhibits both high stability and small interfacial resistance with commercial organic liquid electrolytes, which makes it promising as a separator in Li-ion batteries.